A bit error rate (BER) analysis for the Non-linear Optical Loop Mirror (NOLM) demultiplexer is presented using a combined optical receiver and NOLM model. The control pulse used in the NOLM model is assumed to be of soliton shape in order to obtain a flat-top switching window to reduce the effect of timing jitter between the control and signal pulses. The NOLM model is incorporated into an optical receiver model for a bit error rate (BER) analysis. It is found that noise due to timing jitter, cross-talk and BER are strongly dependent on the walk-off time between the control and signal pulses in the NOLM demultiplexer. Results show that the power penalty of a NOLM demultiplexer using a soliton control pulse can be minimized with an optimum value of walk-off time. In addition the cross-talk of the Terahertz Optical Asymmetric Demultiplexer (TOAD) has been investigated using a TOAD model. Simulation results show that the cross-talk of a TOAD increases as the asymmetry time is increased. A comparison of the two devices for 100 Gb/s demultiplexing shows that the cross-talk of a TOAD (with an optical amplifier recovery time of 300 ps) is at least 3 dB lower than that of NOLM for maximum demultiplexed output.